The present invention relates to a display device employing a plasma display panel that displays television images and so forth and, particularly, to a display device that can improve a reduction in color temperature accompanying deterioration of fluorescent materials caused by electrical discharge in the plasma display panel.
A plasma display panel display device using a plasma display panel (hereinafter referred to as “PDP”) is a variation of display devices having a low profile and capable of displaying television images and so forth. The PDP display device is suitable for a large screen display and, therefore, attracts public attention.
The PDP utilizes the excited emission phenomenon of fluorescent materials induced by ultraviolet rays that are generated by discharge of a rare gas such as Ne (neon), Xe (xenon) and the like. FIG. 7 is a perspective view showing an example of a panel configuration of an AC type PDP. In FIG. 7, reference numeral 100 denotes a PDP; 101 denotes a glass substrate that is a substrate on the display face side; 102 denotes a pair of display electrodes formed on the glass substrate 101, the pair of display electrodes consisting of an X display electrode 102x and a Y display electrode 102y, each of the X and Y display electrodes consisting of a transparent electrode 120a and a metal assist plate 120b for reducing resistance. Reference numeral 103 denotes a dielectric layer covering the pair of display electrodes 102; 104 denotes a protection film made of MgO covering the pair of display electrodes 102 and the dielectric layer 103. Reference numeral 121 denotes a back face side glass substrate disposed to oppose to the glass substrate 101; 125 denotes address electrodes disposed on the glass substrate 121 in the form of stripes; 122 denotes partitions disposed adjacent to the address electrodes. Reference numeral 123 denotes fluorescent materials applied to the address electrodes 125 to cover them. A red fluorescent material (R), a green fluorescent material (G) and a blue fluorescent material (B) are applied to three address electrodes, respectively, which constitute a pixel. Reference numeral 124 denotes discharge spaces enclosed by the partitions 122 disposed between the substrate on the display electrodes side and the substrate on the fluorescent materials side. Each of the discharge spaces is filled with the rare gas such as Ne, Xe or the like. Discharge cells shown in FIG. 9 are arranged in the form of a matrix.
FIG. 8 is a schematic diagram showing a discharge mechanism of the PDP, wherein parts shown in FIG. 7 are denoted by the same reference numerals and the explanation thereof is omitted. In FIG. 8, a voltage is applied from a driving circuit (not shown) to each of the address electrodes 125 and the Y display electrode 102y (this operation will be referred to as “address drive” in the following description) to allow a pilot discharge (this discharge will be referred to as “address discharge” in the following description). In addition, a voltage (this voltage will be referred to as “sustain voltage” in the following description) is applied to each of the X display electrode 102x and the Y display electrode 102y (this operation will be referred to as “sustain drive” in the following description) to sustain the discharge (this discharge will be referred to as “sustain discharge” in the following description). The discharges in the discharge space 124 caused by the application of voltages to the electrodes described above cause ultraviolet rays that excite the fluorescent materials 123 to generate red light, green light and blue light, and the light passes through the transparent glass substrate disposed on the display electrodes side.
FIG. 10 shows a display method of the PDP. Since it is difficult for the PDP to display a halftone between emission and non-emission, generally, the PDP employs a method called “subfield method” to display the halftone. In the subfield method, a time span for one field is divided into a plurality of subfields (SF), and a specific emission weight is assigned to each of the subfields to control the emission and the non-emission of each of the subfields, thereby achieving a gradation in brightness of the field. One subfield consists of control pulses for controlling: a reset period for initializing a state of a discharge cell; an address period for controlling lighting/non-lighting of the discharge cell; and a sustain period for determining an emission amount. In FIG. 10, one field is divided into eight subfields (SF1 to SF8) since about 256 gradations (8 bits) are required for achieving display without deteriorating the image signals, and a number of sustain discharges is so set that a relative ratio among brightness during the sustain discharges of the subfields will be 1:2:4:8:16:32:64:128. A sustain voltage waveform applied to each of the X and Y display electrodes for the sustain discharge has a rectangular shape, and the number of sustain discharges described above is equal to the number of pulses applied for the sustain drive (hereinafter referred to as “number of discharge pulses”). Combination of the emission and the non-emission by the subfield unit as explained above allows the setting of the brightness of 256 gradation levels of from 0 to 255 for each of the colors R, G and B. In FIG. 10, the reset period is included in the address period to simplify the drawing.